1. Fire Tubes: In fire tube boilers, the heating surface consists of a bundle of tubes surrounded by hot combustion gases. The hot gases pass through these tubes, transferring heat to the water surrounding them.
2. Water Tubes: In water tube boilers, the heating surface is made up of tubes that carry water and hot combustion gases flow around the outside of these tubes. The heat is transferred from the hot gases to the water inside the tubes.
3. Furnace Walls: The furnace walls, which enclose the combustion chamber, also act as heating surfaces by absorbing heat from the hot gases and transferring it to the water inside the boiler.
4. Superheater Tubes: In some boilers, superheater tubes are used to heat the steam further after it has been generated. These tubes are located in the path of the hot combustion gases or flue gases, and they help increase the steam temperature above its saturation point.
5. Economizer Tubes: Economizer tubes are used to recover heat from the flue gases exiting the boiler. These tubes are typically installed in the path of the flue gases before they are discharged to the atmosphere. By cooling the flue gases, economizers preheat the feedwater entering the boiler, reducing fuel consumption.
The combination of these heating surfaces ensures efficient heat transfer and steam generation in a boiler. The design and configuration of the heating surfaces depend on the specific boiler type, fuel used, and desired steam temperature and pressure.
